DESCRIPTION: (Applicant's Abstract) This application requests 3 years of funding to conduct a comprehensive study of new injection drug users. These users are a barrier to the containment of the AIDS epidemic but for the most part have been overlooked by investigators and interventionists. A cross-sectional research design with a nested case-control study and a nested ethnography is proposed to collect quantitative and qualitative data. The study will describe and compare African American, Hispanic, and white non-Hispanic men and women who are new injectors with other longer term injectors and with other non-injection drug users. A stratified sample of 900 street-recruited drug users (300 within each user group) will be enrolled in the study from which a nested stratified sample of 126 (43 within each user group) will be selected for the ethnography. There are three specific aims: 1) Estimate and compare the seroprevalence of HIV-1 among these three groups of users. Standard epidemiological techniques will be employed. 2) Describe, model, and compare the HIV-1 related injection and sex risk behaviors of these three groups of users. Both quantitative (structured interview) and qualitative (audio-taped interviews and field observation) methods will be employed. 3) Identify the factors associated with the initiation of injection drug use, and identify and describe distinct types of new injectors. A case-control study of new injectors and other non-injection drug users will model factors for the initiation of injection using standard case-control methodology. An ethnography of the process of becoming an injector will be conducted. Gender specific and race/ethnicity specific analyses will be conducted for each specific aim. The ultimate objective is to provide a comprehensive understanding of new injectors which will more fully specify the personal and social characteristics and circumstances that represent the most appropriate target for intervention programs.